During a procedure (hereinafter, referred to as a “flow”) for transmitting/receiving packets between an evolved Node B (eNB) and a User Equipment (UE) in a mobile communication system, each packet is retransmitted several times by a Hybrid Automatic Repeat reQuest (HARQ) process in order to reduce errors in a wireless section. When an eNB or UE transmits a packet in an Unacknowledged Mode (UM) of Radio Link Control (RLC), only HARQ retransmission is performed. In contrast, when the eNB or UE transmits a packet in an Acknowledged Mode (AM) of RLC, HARQ retransmission is performed, and ARQ retransmission is performed when the performed HARQ retransmission has failed.
An HARQ parameter, which is connected with the end-to-end performance of a flow in the eNB or UE, includes a maximum-number-of-retransmissions parameter maxHARQ-Tx, and an ARQ parameter includes a maximum-number-of-retransmissions parameter maxRetxThreshold and a plurality of timer parameters, that is, t_Reordering, t_StatusProhibit, and t_PollRetransmit. Here, the HARQ parameter and ARQ parameter are set to the same values in every flow by Radio Resource Control (RRC) of an eNB or UE.
When an eNB sets HARQ and ARQ parameters to the same values for all UEs without taking the channel status of each UE into consideration, as described above, it may exert a bad influence on the communication performance in a UM and/or AM according to the channel status of each UE. For example, when an eNB sets the HARQ and ARQ parameters based on an average channel status, an HARQ retransmission using the set HARQ parameter is performed even in the case where a channel is in a bad status, so that the probability of failure in the HARQ retransmission increases, and the communication performance in a UM is deteriorated. Also, in this case, since the number of ARQ retransmissions increases in an AM due to the failure of HARQ retransmission, delay time becomes longer, and the error rate also increases due to the set ARQ parameter, that is, due to the number of retransmissions.
Also, when an eNB independently sets the ARQ parameter without taking a preset HARQ parameter into consideration, it may exert a bad influence on the communication performance in an AM. For example, the eNB may perform an ARQ retransmission before an HARQ retransmission is terminated, or the t_StatusProhibit timer for an ARQ may not expire when the HARQ retransmission has been finished, thereby causing an unnecessary delay.
Accordingly, it is necessary to develop a method for setting HARQ and ARQ parameters optimized according to the channel status of each UE in a mobile communication system.